HEMODILUTION INDUCES STABLE CHANGES IN GLOBAL CARDIOVASCULAR AND REGIONAL MYOCARDIAL-FUNCTION

The cardiovascular responses associated with isovolemic hemodilution h ave been described. However, the stability of these responses over tim e remains controversial. We hypothesized that the hemodynamic response s to isovolemic hemodilution are stable over time. Nine fentanyl-midaz olam-anesthetized dogs were monitored to follow global cardiovascular and regional myocardial function. Isovolemic hemodilution was performe d to a moderate (hemoglobin = 7.5 g%) target hemodilutional state that was maintained for 4 h. Data were obtained at each hemodilutional sta te and each hour during the 4-h period of sustained moderate hemodilut ion. During acute hemodilution, cardiac output increased from 2.6 +/- 0.5 L/min to 3.0 +/- 0.5 L/min (P < 0.05) and mean coronary flow incre ased from 20.8 +/- 2.4 mL/min to 31.4 +/- 5.5 mL/min (P < 0.05). Cardi ac output and mean coronary flow remained elevated during the extended hemodilutional period. In addition, norepinephrine increased from 586 +/- 152 pg/mL to 1135 +/- 247 pg/mL (P < 0.05) during acute isovolemi c hemodilution and remained at this increased level during extended he modilution. Epinephrine levels did not change with hemodilution. Compe nsatory mechanisms such as increases in cardiac output and mean corona ry flow observed during acute hemodilution persist during extended per iods of hemodilution.